In the broadcast and communication field, data is transmitted in blocks with a predetermined length such as frames. A receiver detects an identifier of a frame synchronization signal or the like stored in transmitted data for each frame and performs demodulation processing for each frame by the frame synchronization signal or the like.
For example, in DTMB (Digital Terrestrial Multimedia Broadcast), which is a digital terrestrial broadcast standard of China (People's Republic of China), a frame is configured by a frame body (hereinafter referred to as an FB) and a frame header (hereinafter referred to as an FH). In an FB, 3780 symbols are stored which are combination of modulated source stream data and system information. In the FH, a quasi-random noise sequence (hereinafter referred to as a PN sequence) is stored as a known signal for identifying the frame. The DTMB has three kinds of FH length and has first to third broadcast modes corresponding to the three FH lengths.
There is a technique of inputting a received signal converted to a frequency-domain signal, as a received signal of a receiver, and detecting a frequency error by determining correlation between this received signal converted to the frequency-domain signal and a known signal inserted into the frequency-domain signal and determining an amount of change from a reference value.
On the other hand, there is a technique of inputting a received signal converted to a time-domain signal, as a received signal of a receiver, frequency-converting the received signal converted to the time-domain signal as well as frequency-converting a known signal inserted in the time-domain region, estimating influence of distortion of the frequency-converted known signal caused in a transmission line, and correcting periodic distortion (a frequency error) of the received signal on the basis of the estimated value.
However, in the case of detecting frequency distortion (an error) by causing a time-domain received signal to be a frequency-domain signal by frequency conversion in the DTMB, as described before, a frequency conversion circuit corresponding to the length of a time-domain known signal is required. In the DTMB, three kinds of frame header (FH) (symbol lengths: 420, 595 and 945) are prepared as the FH of a time-domain received signal. In the case of frequency-converting an FH to use it, at least four kinds of frequency conversion circuit, including three frequency conversion circuits corresponding to the three kinds of FH signals and one frequency conversion circuit for frequency-converting a frame body (FB) with a symbol length of 3780, and there is a problem that the circuit scale is increased.
A problem to be solved by the present invention is to provide such a frequency error detection apparatus that a frequency conversion circuit can be small-sized, and thereby, the circuit scale can be reduced, in the case of detecting frequency distortion (an error) by causing a time-domain received signal to be a frequency-domain signal by frequency conversion.